1. Field of the Invention
The present invention relates to a home position storage unit and a home position storage method for bringing a printing cylinder into a stop at an appropriate plate replacement position during operation for replacing a plate of the printing press.
2. Description of the Related Art
In the recent printing industry, great needs for high-value-added, small batches of a variety of products exist, and a shorter delivery time is strongly requested. In such a trend, a shorter print preparation time as well as speedup in printing operation are required of the printing press. Under circumstances of the great needs for small batches of a variety of products, opportunities for replacement of a plate have increased more than ever. Shortening a time to replace a plate has hitherto posed a problem. In order to solve this problem, Japanese Patent No. 2704558 discloses a technique for automatically replacing a plate.
As described in Japanese Patent No. 2704558, in a printing press that automatically replaces a plate, a printing cylinder needs to be stopped at an appropriate plate detachment position or an appropriate plate attachment position with respect to a rotating direction, in order to perform removal or supply of a plate. Although not described in Japanese Patent No. 2704558, there is operation for storing the home position of a printing cylinder in order to stop the printing cylinder at the plate replacement position. This operation is for, when a command for automatically replacing a plate is issued to the printing press, accurately ascertaining the rotating position of the printing cylinder and bringing the printing cylinder into a stop at an appropriate plate replacement position by means of: detecting passage of a cam provided on the rotating printing cylinder through use of home position sensors provided on respective printing units; and extracting detection information from a position sensor for detecting a pulse from an encoder that produces a pulse in synchronism with rotation of a driving device of the printing press achieved at the time of detection of the passage. Since the printing cylinder has a mechanism for finely adjusting a top-and-bottom direction and others, as a result of performance of fine adjustment, a relative position between the cam provided on the printing cylinder and the home position sensor changes before and after fine adjustment, thereby ending in a failure to bring the printing cylinder into a stop at an appropriate plate replacement. Accordingly, the home position must be stored every time a plate is automatically replaced. In addition, even when the operator has opened covers of respective printing units, and the printing cylinders cannot come to a stop at the appropriate plate replacement position. Hence, the home positions must be stored. In relation to storage of the home position, the home position is stored, under the related-art method, every time a command for automatic replacement of a plate is issued. However, this means that the home position cannot be stored unless the cam provided on the printing cylinder passes by the home position sensor after issuance of the command for automatic replacement of a plate. There has been a problem of automatic replacement of a plate involving consumption of much time and being contrary to the desire for a shorter preparation time for printing.